Responses of the photosynthetic system of drought-tolerance weedy rice to drought stress at the seedling stage

Drought is the most important abiotic stress constraint responsible for reducing yield in most rice-producing areas. Weedy rice is considered an important germplasm resource for rice improvement,because it has many useful genes conferring abiotic stress tolerance. The objective of this study was to elucidate the different drought-stress responses of drought-tolerance weedy rice( HEB07-2),common weedy rice( WR04-6),upland rice( iapar9),and drought-sensitive cultivated rice( yuefu),with respect to the photosystem,leaf temperature,and water use efficiency after 5,24,or 72 h of treatment. The results show that 72 h of drought stress has almost no effect on the total chlorophyll content of iapar 9 orWR04-6,but reduced the chlorophyll content of the drought-sensitive variety,and increased the chlorophyll content of HEB07-2. Maximum fluorescence(F_m) and maximum quantum efficiency( Fv/ F_m) were both reduced in plants exposed to drought,whereas the initial fluorescence( F_o) was elevated. Our analysis indicated that under drought conditions,photosystem II was damaged,with the injury to the drought-sensitive variety yuefu being much more serious than that incurred by the drought-tolerance weedy rice HEB07-2. The start time of F_oincreased and that of F_mdecreased,being later in HEB07-2 than in other genotypes. This indicates that HEB07-2 was injured later than others. The photosynthetic rate and stomatal conductance decreased with increased drought,but the change occurred more slowly in weedy rice HEB07-2than in the cultivar yuefu. Plant population temperature changes were measured using an infrared camera,with the leaf temperature of yuefu and WR04-6 increasing significantly under drought stress,while that of HEB07-2 and the upland rice cultivar iapar9 did not change significantly. Under drought stress,the malondialdehyde( MDA) content of yuefu increased much more than that of other genotypes. MDA content of HEB07-2 increased the least,indicating that it experienced less severe injury. The results indicate that HEB07-2 and iapar9 were the most drought-tolerant,and yuefu was the least drought-tolerant. In conclusion,the variation among the weedy rice and cultivated rice cultivars tested suggests that there are valuable genetic resources for improving the drought-tolerance of rice.